FIG. 1 shows a conventional vehicle panel 90 that includes a decorative coverstock material 112, a coverstock foam layer 114, an air-impermeable adhesive barrier layer 116, a lower glass mat layer 120, a core foam layer 130, an upper glass mat layer 160, and a scrim layer 140. The upper glass mat layer 160, the core foam layer 130, and the lower glass mat layer 120 are adhered together using a thermosetting adhesive, such as, for example methylene diphenyl diisocyanate (“MDI”), along with a catalyst, which can be sprayed on or rolled on to the core foam layer 130, between the upper glass mat layer 160 and the core foam layer 130 and between the lower glass mat layer 120 and the core foam layer 130 to form a rigid composite reinforcing layer. Because the process uses a thermosetting adhesive, such as MDI, as opposed to using an adhesive film or a hot melt adhesive to bind the upper glass mat layer 160 and lower glass mat layer 120 to the core foam layer, the adhesive flows through the upper glass mat layer 160 and lower glass mat layer 120. This is advantageous, as the upper adhesive layer can also be used to adhere a coverstock laminate 105, comprising the decorative coverstock material 112, the coverstock foam layer 114, and the adhesive barrier 116, to the lower surface of the upper glass mat layer 160. In many cases, the adhesive barrier 116 is the same as the scrim layer 140.
The composite headliner is formed by placing the various layers, including the coverstock laminate, between two plates of a press and applying heat and pressure to the stack of layers. The pressure forces the MDI adhesive through the upper glass mat layer 160 and lower glass mat layer 120 to adhere the various layers together, while the heat and the catalyst causes the MDI adhesive to cure or set and forms the composite matrix.
However, at the same time, if not prevented, the MDI adhesive can flow to areas where it is not desired. Specifically, such areas include the tool surfaces used to heat and compress the various layers and the decorative coverstock composite material. In particular, the MDI adhesive can mar or otherwise negatively affect the appearance of the surface of the decorative coverstock material if it were allowed to reach the decorative coverstock material 112 or the coverstock foam 114, such as, for example, by causing pits, bumps, adhesive bleed through, and ripples in the surface. Accordingly, the scrim layer 140 and the adhesive barrier layer 116 protect the tool surfaces and the decorative coverstock material 112 and coverstock foam layer 114, respectively, by preventing the MDI adhesive from flowing past the scrim layer 140 and adhesive barrier layer 116.